@ binding
- Rust course
- Advanced
- Lesson 74/81
- 4 min
Bind a value range with the @ operator.
@ binding
name @ pattern checks a value against the pattern while binding it to a variable at the same time. It's handy with ranges and nested patterns:
fn basamak(n: u32) -> String {
match n {
k @ 0..=9 => format!("tek basamak {k}"),
k @ 10..=99 => format!("iki basamak {k}"),
k => format!("büyük {k}"),
}
}
match opt {
Some(x @ 1..=5) => println!("küçük: {x}"),
Some(x) => println!("diğer: {x}"),
None => {}
}Without @, a range pattern wouldn't bind the value and the arm would have to reuse n.
Together with |
@ works with patterns that have several alternatives too; all alternatives must bind the same variable:
match karakter {
c @ ('a' | 'e' | 'ı' | 'i' | 'o' | 'ö' | 'u' | 'ü') => println!("sesli {c}"),
c @ ('0'..='9') => println!("rakam {c}"),
c => println!("diğer {c}"),
}Practice Digit class
Write the basamak function above with @ bindings. Print the results for 7, 42 and 500 on separate lines.
Starter code
fn main() {
// buraya yaz
}Sample solution
fn basamak(n: u32) -> String {
match n {
k @ 0..=9 => format!("tek basamak {k}"),
k @ 10..=99 => format!("iki basamak {k}"),
k => format!("büyük {k}"),
}
}
fn main() {
for n in [7, 42, 500] {
println!("{}", basamak(n));
}
}Expected output
tek basamak 7 iki basamak 42 büyük 500
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does the pattern <code>e @ Mesaj::Yaz(_)</code> bind?
- It doesn't compile
- The whole Mesaj::Yaz value to e Correct answer
- Only the inner text
- Nothing
Explanation: @ binds the whole value; if the inner part is needed too, they can be written together like e @ Mesaj::Yaz(ref m).
2 Bind with a range
match n {
k ____ 0..=9 => format!("tek basamak {k}"),
k => format!("{k}"),
}match n {
k @ 0..=9 => format!("tek basamak {k}"),
k => format!("{k}"),
}Explanation: @ both checks the range and binds the value to k.
3 Number and basamak result
| Term | Meaning |
|---|---|
7 |
tek basamak 7 |
42 |
iki basamak 42 |
500 |
büyük 500 |
0 |
tek basamak 0 |